1. Field
The present technology generally relates to a method for manufacturing a positive temperature coefficient (PTC) device and a system for preventing overheating of a planar heater using the same, wherein a plurality of PTC devices are connected in series and are thus used as an overheating prevention sensor of a planar heater controller to control electric-current transfer of the planar heaters, when over-heating (or heat storage) occurs, to improve safety of the planar heaters.
2. Description of the Related Art
Most flooring heating and other heating systems to date have generally used fossil fuels such as oils and gases, thus entailing serious problems such as exhaustion of fossil fuels as well as environmental pollution caused by toxic gases generated upon incomplete combustion. For this reason, heating systems using alternative energy are attracting much attention, and research and development thereof have been continued. As a result, electric heating appliances using electricity instead of fossil fuels were developed and are commonly used. However, heat-generation using electricity developed to date mainly uses local heating caused by heating resistors, arcs or induction heating, or one-dimensional linear heating. These heat-generation methods disadvantageously involve concentration of heat only around a heating source, thus requiring homogeneous heat-generation throughout wide two-dimensional plains in view of the efficiency. As a result of a great deal of research for novel heating sources, planar heaters have thus been developed.
A planar heater generates heat, based on an electric current applied to thin-film electrodes, which are inserted into both terminals thereof, and inherent resistance of a material thereof. The planar heater is applied to various shapes of heating systems (heating systems for floors, walls, cells, etc.) and industrial heater components, and thus attracts much attention as next-generation heating source for heating systems which enable homogeneous heat-generation throughout wide two-dimensional planes owing to superior flexibility. Thus, such heaters realize economical and friendly-environmental effects by replacing fossil fuels.
The most generally used temperature-control manner for planar heating is electricity control using a temperature sensor. The principle of this manner is to control heat-generation, based on the temperature displayed on a temperature-sensor mounted on the surface of a heater. When a planar heater is applied to floor heating systems, heaters most generally control temperature based on the temperature measured using a temperature sensor (such as thermistors or bimetals) adhered to the surface of a heater.
One problem with this temperature-control method relates to control of the overall temperature throughout the system, based on the temperature around the sensor. This problem is negligible, when the overall surface maintains a predetermined temperature, but a predetermined part except for the sensor stores (or collects) heat and requires caution of users in order to prevent damage to finishing materials and products. An example of damage to finishing materials and deterioration in product performance caused by heat storage (heat accumulation) will be illustrated. In ordinary life, blankets, cushions and materials for blocking heat in the air are exposed to a region spaced from sensors for controlling temperature for a long time, thus disadvantageously causing rapid elevation in temperature, as compared to a control temperature and then damage to finishing materials and deterioration in product performance.
That is, the heater is controlled by measuring only a region in which the temperature sensor is arranged, thus causing the difference in temperature between a region close to the temperature sensor and a region far therefrom depending on the external heat-insulation level and the surrounding temperature, and requiring care of users such as unlimited generation of heat from the heater. More specifically, when blankets, cushions and materials for blocking heat are placed in absence of temperature sensors for a long time, the temperature is rapidly elevated, as compared to a control temperature, and finishing materials may be damaged or product performance may be deteriorated.
In order to solve these problems, it is preferable to prevent excessive elevation in temperature by controlling the temperature throughout the planar heater.
Conventional multichannel temperature sensing methods have a limitation of system development and construction. For multichannel temperature sensing methods, it is not easy to control temperature of a wide area, based on data received from respective channels. When one of a plurality of temperature sensors operates abnormally, it may affect the overall system, thus causing difficulty in finding optimum heating conditions and considerably lowering practical applicability. Also, this method has the disadvantage of complicated structures of heating systems, thus making it difficult to install and construct, and causing an increase in construction costs.
In addition, positive temperature coefficient (PTC) heaters (positive temperature heating elements) are mostly small heaters having a narrow electrode gap and PTC heaters for heating are generally applied to ultra-small areas of constructions, but are relatively expensive and are generally limited to low-voltage products. This is the reason that products may be readily damaged due to deterioration of PTC heaters and thus limited reproduction of PTC performance, when a high voltage (AC 100V or higher) is repeatedly applied in order to heat PTC heaters.